Although the broad outlines of teleost immunity are known, the lack of molecular information concerning key cell surface markers (e.g. CD3, CD4, CD8) and cytokines (e.g. interferons and interleukins) has slowed progress. This collaborative pilot study intends to address this deficiency and to identify genes for catfish immune regulatory proteins and cell surface markers by differential display. To identify immune regulatory proteins, catfish peripheral blood leukocytes (PBLs) will be induced to express immune function genes and mRNAs from activated cultures will be compared to mRNAs from untreated cultures by differential display. RNAs from both populations will be reverse transcribed using arbitrary primers, amplified, resolved on sequencing gels, and visualized by autoradiography. After cloning and sequencing the amplicons, selectively expressed in activated cultures, their nucleotide or deduced amino acid sequences will be compared to known genes or gene products by BLAST analysis to determine whether differentially expressed amplicons encode immune-related gene products. To obtain full-size transcripts, amplicons encoding immune-related genes will be used to screen a cDNA library prepared from activated cultures. Putative immune functions will be characterized by Southern blot analysis to determine the number of copies per genome and Northern blot analysis to determine levels of constitutive and induced expression and the kinetics of expression. Genes of interest will be expressed and the resultant recombinant proteins used as antigen to develop specific antibodies. Western blot analysis will determine when, following induction, the protein is expressed and immunological staining will determine cell and tissue sites of expression. Successfully completed, this study will provide important new information that will further understanding of teleost immune responses, and perhaps provide insight into the origins of human immunity.